Although a practitioner may obtain a sample of a fluid from a medical or veterinary patient and order a variety of laboratory tests thereon, the processing of the sample in the clinic, its transportation to the laboratory, processing and analysis in the laboratory, and reporting of results all cause delay and expense. In some cases, it is desirable for the clinician to obtain an immediate and reliable indication of one or more characteristics of a fluid obtained from a patient.
For example, when inserting a nasogastric tube, the tube may be undesirably positioned in the patient's lungs, instead of the stomach. Introduction of fluid which was intended to be introduced into the patient's stomach into the lung instead may be disastrous. However, correct insertion of the nasogastric tube in the stomach may be confirmed by aspirating fluid through the tube and measuring the pH of the fluid. A pH below 6 is characteristic of stomach fluid and signals the clinician that the tube has been correctly inserted.
Although there are a variety of supplies and equipment that could, in theory, be used in a clinical setting to measure a fluid characteristic, it is not always convenient or safe to perform reliable and accurate measurements. Test equipment may not necessarily be available in the clinic at the time it is needed, may require calibration or preparation of the equipment or accessories before use, cleaning after use, or non-trivial training of personnel for correct measurement, operation, and interpretation of the result. Also, the cost of some equipment makes it unaffordable in some clinics. The test results may be needed immediately, which can make obtaining and interpreting an accurate measurement challenging. Also, the sample itself may be unstable, either generally, over time, or as a result of exposure to air, test probes, containers, reagents, materials, or the like, which allows only limited time for performing a measurement. Some test equipment or procedures require that the sample be handled in the open, which can result in spills and exposure of personnel to the sample, which may present chemical, biological, or radiological hazards.